Compliant supports for transducer diaphragms



'8, 1953 L. c. POCOCK 2,646,853

COMPLIANT S UPPORTS FOR TRANSDUCER DIAPHRAGMS Filed NOV. 5, 1949 8 I F/G'2. a

Inventor LC. PQC UCK Attorney Patented July 28, 1953 UITED STATES .ENT OFFICE COMPLIANT SUPPORTS FOR TRANSDUCER DIAPHRAGMS Delaware Application November 5, 1949, Serial No. 125,671

In Great Britain November 11, 1948 6 Claims.

The invention relates to peripheral supporting means for vibratory diaphragm electro-acoustic transducers.

Diaphragms for such vibratory devices are usually required to have the largest possible effective area, a large supporting compliance over limited displacements and the diaphragm edges must be effectively connected to a frame or support so as to avoid air leakage. The first requirement quoted is equivalent to a substantially piston-like movement of the diaphragm. In order to achieve such piston-like movement, the edges of the diaphragm should have the high compliance previously quoted as a requirement for such diaphragms.

One known method of satisfying this requirement uses a diaphragm comprising a thin, rigid central portion fastened to an annulus of high compliance. In such a device the rigid centre portion moves with piston-like motion and the annulus provides a high degree of compliance. This method has the disadvantage of requiring an awkward manufacturing process in that it is difiicult to stick the annulus to the rigid portion reliably.

The object of the present invention is to provide a diaphragm structure superior to those constructed by known processes, and in which difficult manufacturing problems are eliminated.

The main feature of the present invention comprises a vibratory diaphragm having an outer annular face on one side of the diaphragm which is held in substantially air-tight contact against an unsupported portion of a peripherallymounted compliant membrane or annulus by compliant means acting on the other side of the diaphragm.

The invention will now be particularly described with reference to the accompanying drawings in which Figs. 1 to 4 show, partly in section, four embodiments of the present invention.

Referring first to Fig. 1, a diaphragm is shown driven from (or driving) the armature assembly by a connecting rod 2. The diaphragm I is formed with a conical portion 3 and a flat annulus ii at the extreme edge of the conical portion 3. The diaphragm I is constructed of some rigid material such as an aluminium alloy. The flat annular portion 4 of the diaphragm I is gripped between two compliant annuli 5 and 6. These annuli may be made of polystyrene, rubber, or some other suitable non-porous plastic sheet material. Of these polystyrene has been found to be particularly suitable on account of its high degree of compliance. The annuli 5 and B which provide the compliant support for thediaphragm are held between two annular clamping-rings I and 8 fastened together by any suitable means, not shown.

In such an assembly the diaphragm is selfcentering and is thus able to take up small errors in position of the connecting rod. It will be appreciated that the diaphragm can make slight side-ways excursions within its compliant supports. This is particularly desirable in the case of a balanced armature unit of the type described in our British Patent No. 606,012 (Roberton 18), as the armature of such a device imparts a slight sideways motion to the connecting rod in addition to the main component of motion in a line with the axis of the diaphragm. This sideways component may thus be taken up without producing any distortion due to unwanted modes of vibration. Furthermore, the system is less affected by extraneous forces not in line with the axis of the cone.

In Fig. 2, the lower compliant annulus 6 of Fig. 1 is replaced by a membrane 9 of some compliant, non-porous material. In one particular form of Fig. 2, the diaphragm consisted of an alloy of 93% aluminium and 7% magnesium, the annulus consisted of a ring of polystyrene .002" thick and the membrane of polythene .002" thick. Polythene is particularly suitable for a membrane for a vibratory diaphragm because it is slightly stiffer than polystyrene and moreover it has very good water-resistant properties. This structure provides a particularly suitable diaphragm assembly for small units such as those required for telephone receivers and transmitters.

In the embodiment depicted in Fig. 3, the diaphragm is lightly pressed against the membrane 9 by a spiral spring it on the connecting rod 2 anchored by a block ii. The spring [0 could be replaced by a leaf-spring. The membrane 9 could, of course, be replaced by an annulus of any suitable compliant material.

The embodiment shown in Fig. 4 is somewhat similar to that of Fig. 2 from which it is derived. The annulus 5 is replaced by an annular pad 12 of some compliant material such as felt, rubber or polyvinyl chloride. The upper damping ring 1 of Fig. 2 is replaced by an annular member [3 of L-shaped cross-section to receive the pad I2. The membrane must be non-porous, but no such limitation applies to the pad. It will be understood that in this embodiment the membrane 9 could be replaced by a compliant annulus.

While the principles of the invention have been described above in connection with the specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is mad only by way of example and not as a limitation on thescope of the invention.

What is claimed is:

1. An electro-acoustic transducer including a conical diaphragm of inherently rigid material, armature means associated with the apex of said diaphragm in a manner to drive or to be driven by said diaphragm, a marginally supported circular membrane of a compliant material, said diaphragm being concentrically disposed in respect to said membrane and in marginal contacting engagement therewith, and an annular element of compliant material. of an overall diam eter equal to the diameter of said membranewith outer portions thereof clamped in contiguous registered engagement with the outer portions of said membrane and inner portions thereof extending over the margin of said diaphragm on the side thereof opposite to that which marginally engages said membrane, whereby said diaphragm is floatably positioned between said membrane and said compliant annular member to permit transverse displacement thereof for centering of said armature, said membrane beingof sufiiciently thin and compliantmaterial to conform to and thereby not interfere with sound waves initiated by said diaphragm and traveling toward, and effectively through and outwardly from said membrane.

2. The transducer of claim 1 wherein said diaphragm is of compliant, non-porous plastic sheet material.

3. The transducer of claim 1 wherein said membrane comprises a thin sheet of polythene.

4. The transducer of claim 1 wherein said diaphragm and said annular compliant member comprises a thin plastic sheet material.

5. The transducer of claim 1 wherein said annular compliant member is of polystyrene of a thickness of a few thousandths of an inch.

6. The transducer or claim 1 wherein said diaphragm is of inherently rigid metallic sheet stock and said membrane comprises a thin sheet of compliant plastic material.

LYNDALL CROSSTHWAITE POCOCK.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,554,794 De Forest Sept. 22, 1925 1,734,271 Peterson Nov, 5, 1929 1,738,955 Jordan et al. Dec. 10, 1929 1,745,686 Moore Feb. 4, 1930 1,877,804 Bruijnes Sept. 20, 1932 FOREIGN PATENTS Number Country Date 293,414 Great Britain Mar. 4, 1929 

